1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting diode (LED) in which an electron emitting layer having excellent crystallinity is grown so that light emission efficiency and ESD (electrostatic discharge) characteristic of the LED can be enhanced.
2. Description of the Related Art
Generally, nitride semiconductors are widely used in green or blue light emitting diodes which are provided as light sources in full-color displays, image scanners, various signal systems, and optical communication equipments. Such a nitride semiconductor LED includes an active layer disposed between n-type and p-type nitride semiconductor layers, the active layer having a single quantum well (SQW) structure or a multi-quantum well (MQW) structure. In the active layer, electrons and holes are recombined so as to generate and emit light.
Hereinafter, a conventional nitride semiconductor LED will be described in detail with reference to FIG. 1.
FIG. 1 is a sectional view illustrating the structure of the conventional nitride semiconductor LED. As shown in FIG. 1, the nitride semiconductor LED includes an optically-transparent sapphire substrate 110, an n-type nitride semiconductor layer 120, an active layer 140 containing InGaN with a single quantum well (SQW) structure or a multi-quantum well (MQW) structure, and a p-type nitride semiconductor layer 150, which are sequentially laminated on the sapphire substrate 110.
Portions of the p-type nitride semiconductor layer 150 and the active layer 140 are removed by mesa-etching such that a portion of the upper surface of the n-type nitride semiconductor layer 120 is exposed. Further, on the exposed upper surface of the exposed n-type nitride semiconductor layer 120, a negative electrode (n-electrode) is formed. On the surface of the p-type nitride semiconductor layer 150, a positive electrode (p-electrode) is formed.
In the multi-quantum well structure having a plurality of mini-bands, the efficiency thereof is excellent, and light emission can be performed by using a small current. Therefore, the multi-quantum well structure has a larger light-emission output than the single quantum well structure, which makes it possible to expect the enhancement of diode characteristics.
In such a conventional nitride semiconductor LED, an electron emitting layer 130 composed of an InGaN/GaN layer is formed between the active layer 140 and the n-type nitride semiconductor layer 120. The InGaN layer and the GaN layer increase an effective electron number, which is smaller than an effective hole number, by using a tunneling effect, thereby effectively serving as the electron emitting layer 130 which increases a probability of capturing carriers in the active layer 140.
Such an electron emitting layer 130 increases a lattice period through a plurality of slim InGaN/GaN layers. Therefore, the electron emitting layer 130 reduces a driving voltage and increases light-emission efficiency, thereby having a good effect on ESD characteristics.
However, when the InGaN layer is grown, it is difficult to adjust gas pressure, because equilibrium vapor pressure of In is extremely high and equilibrium vapor pressure of NH4 serving as a source gas of N is low. Further, in order to obtain an InGaN layer having excellent crystallinity, the InGaN layer should be grown at high temperature of more than 1000° C. In such a temperature condition, however, most of In is vaporized, which makes it difficult to produce InN. Further, when the temperature is decreased, the quality of InGaN is severely degraded. Therefore, it is very difficult to produce an InGaN layer with a high quality.
Therefore, in this technical field, a new method is being required, in which an electron emitting layer with excellent crystallinity is obtained so that light-emission efficiency and ESD characteristics of an LED can be enhanced.